Finally got my Grand National running right, I can get boost by power-braking, it chirps the tires hard going into 2nd and is getting 16-17psi
of boost. These cars really do run!- My question is: is the 3" downpipe the right choice?
Here's what I've done so far. When I bought the car it overheated and idles good, but just ran doggy (but I had to have it). Ordered new from GM: upper/lower trad hoses, serp belt.& tensioner, heater control valve & heater hoses. Got a 3-core rad. from Nick Micale. Ordered stainless MAF pipe & throttle body inlet (with new hoses & clamps) from ATR, also billet inlet bell & thermostat housing with new thermostat.
I spent the next 2 weekends in a friend's shop, pulled & clean intercooler, replaced crank pully and tensioner, replaced very nasty (original?) thermostat & s-hose. Of course the trans coolant line was corroded and I had to find a replacement.
Upgraded turbo & intercooler inlet hoses with new and new stainless clamps, also new oil cooler lines. Replaced heater control valve & hoses (heater still no work) but running better.
Last week took to Lone star Buick club (Adi) for tuning. The O2 sensor was shot, the previous owner was running split-fire plugs replaced with AC. EGR, PCV & fuel filter replaced. Put on machine, set TPS. now finally the GN runs at the performance level I expect. It is getting 16-17# boost. I have found a used ATR 3"downpipe. with my (mostly stock) combination (it does have a cat-back exhausT) what kind of improvement will I see ith the downpipe, is it worth it?
sorry for the long post.
re
It's my opinion that the 3" pipe will not show you any benefit until you are way into the 12's.
I am not sure which ATR dp you are looking at, but, be warned that some of the ATR clones of the Terry Houston dp have given purchasers a lot of problems with sticky wastegate mechanisms.
I would hold buying such things until you have gained familiarity with parts and what really gives you a bang for the bucks as there are some guys like UNGN from up that direction that run in the 11's without buying a lot of stuff. They follow the recipes listed on this site pretty closely and know what is worth the effort and what is not.
Yeah, what Steve said. Follow the recipes on GNTtype from Ken Mosher and Chuck Strader. The major restrictions in the exhaust system are the cat, mufflers and elbow. A 2.5" dual exhaust, straight thru, low backpressure performance mufflers like ultraflows or max flows, a test pipe and a ported elbow will be within .1 second/2 mph of a THDP with a dump into the high 11's.
Adi's good for general maintenance, but isn't widely known for making a car fast (unless dumping a ton of money in something is his technique). If you are the LSPBC list, meet up with us at a local 1/8 mile and we'll be sure to help you go fast cheaply.
Chris Bischof
http://perfauto.tripod.com